This invention relates in general to automatic transmissions for vehicles and in particular to a reinforcement member for a cylinder in such a vehicular automatic transmission.
In most vehicles, a transmission is provided in the drive train between the engine and the driven wheels. As is well known, the transmission includes a case containing an input shaft, an output shaft, and a plurality of meshing gears which are selectively connected between the input shaft and the output shaft. The meshing gears contained within the transmission case are of varying size so as to provide a plurality of speed reduction gear ratios between the input shaft and the output shaft. By appropriate selection of these meshing gears, a desired speed reduction gear ratio can be obtained between the input shaft and the output shaft. As a result, acceleration and deceleration of the vehicle can be accomplished in a smooth and efficient manner.
Typically, this gear ratio selection is accomplished by moving one or more control members provided within the transmission. Movement of the control member causes certain ones of the meshing gears to be connected between the input shaft and the output shaft so as to provide the desired gear ratio therebetween. In a manual transmission, movement of the control member is accomplished by manual exertion of the vehicle driver, such as through a shift lever. In an automatic transmission, movement of the control member is usually accomplished by a hydraulic actuator in response to predetermined operating conditions.
A typical automatic transmission includes a plurality of control members which are selectively actuated so as to engage different gear ratios for use. In one automatic transmission which is in common use, a low-reverse clutch piston is provided as one of the control members. Movement of the low-reverse clutch piston functions to control the operation of the transmission in either a low gear ratio or reverse gear ratio. The low-reverse piston is disposed within a cylinder for axial reciprocating movement. The cylinder, in turn, is disposed within an annular recess formed in the rear wall of the transmission case. A gasket is provided between the adjacent surfaces of the cylinder and the recess to provide a fluid-tight seal therebetween. The cylinder to the rear wall of the transmission case by a plurality of threaded fasteners which extend through respective apertures formed through the cylinder and the gasket. A feed opening is formed through the cylinder and the gasket to permit pressurized hydraulic fluid to be introduced within the cylinder so as to cause movement of the piston and, consequently, selective engagement of the low and reverse gear ratios.
During use, the magnitude of the pressure exerted by the hydraulic fluid can rise up to about 250 pounds per square inch. Unfortunately, it has been found that such high pressures can cause the portion of the cylinder located about the feed opening to flex or distort. This distortion causes this relatively small annular portion of the cylinder to lose firm contact with the gasket. As a result, undesirable leakage of hydraulic fluid can occur. The leakage reduces the pressure of the hydraulic fluid flowing against the piston and can result in operational problems with the transmission such as, for example, delayed gear engagement, gear slippage, or noise. Thus, it would be desirable to provide an automatic transmission which avoids the problem of distortion of the cylinder and the resultant leakage of hydraulic fluid. It would also be desirable to avoid the distortion problem without requiring modification of the cylinder or piston, allowing easy repair of existing automatic transmissions now in service.